1. Field of the Invention
In one facet, this invention relates to a graft copolymer and repellent composition containing the same, where opposing chemical attributes may be combined into one molecule, such as a hydrophilic portion and a hydrophobic portion. A graft copolymer comprises both a trunk portion and extensions (grafts) from that trunk. In another facet, this invention relates to a method of preparing the graft copolymer, being brought about in a continuous phase using a free radical or ionic initiation to begin a polymerization of extensions from the trunk, where the trunk and graft compositions and the number and length of the grafts are all controlled to deliver specific structures desirable for the graft polymer's end use performance. In an additional facet, the repellent composition of this invention is applied to a substrate, whose end use properties are enhanced by application of the composition in some desirable aspect, such as oil, grease, and/or water repellency. The substrate thus treated also retains desirable properties of its untreated state, such as porosity or surface tactility.
2. Description of the Related Art
Products containing perfluorocarbon groups have a long history of providing fluid repellency to a variety of substrates, including paper, textile, carpet, and nonwoven applications (e.g., “Technology of Fluoropolymers”, J. G. Drobny, CRC Press, 2001, Chapter 6). In particular, fluorochemical-containing treatments have been beneficially used for treating paper substrates for the express purpose of improving the paper's resistance to penetration by grease and oil. This oleophobicity is useful in a variety of paper applications for quick service restaurant food wrap and pet food bags, as well as carbonless fan-apart forms and other specialty applications (“The Sizing of Paper”, J. M. Gess & J. M. Rodriquez ed, TAPPI Press, 2005, Chapter 8)
Graft copolymers may comprise numerous types of structures. Typically, graft and block copolymers are both presented as having long sequences of 2 or more types of monomers. A general discussion of graft copolymers appears in the textbook “Principles of Polymerization”, G. G. Odian, Wiley Interscience, 1991, 3rd edition, page 715-725. This discussion teaches, among several paths, that the ceric (IV) ion may be used to cause trunk polymers containing secondary alcohols, such as cellulose or polyvinyl alcohol, to undergo redox reactions with the ceric ion. The resulting polymer radicals are capable of initiating polymerization, thus creating homo or copolymer branches off of the main polymer chain. The resulting branched copolymer is one type of graft copolymer. Graft copolymers provide a vehicle for combining attributes of widely varying monomers into a structure where those attributes are retained.
Kang-gen Lee et. al. (U.S. Pat. No. 6,136,896) teach graft copolymers using diorganosiloxanes. These graft copolymers, however, are not built from a trunk, as the trunk is assembled during polymerization of various ‘macromonomers’ with other monomers to create the graft copolymer, and do not have application for oil and grease resistance. Matakawa (U.S. Pat. No. 6,503,313) teaches a graft copolymer incorporating fluorinated and siloxane groups. The resulting graft copolymer is similar in structure to that of Kang-gen Lee. The resulting composition finds primary end use in exterior building coatings, and the organic solvent utilized in the polymerization would not make it suitable for the present end uses. Hinterwaldner et. al. (U.S. Pat. No. 5,070,121) teaches a graft copolymer primarily for barrier protection and corrosion resistance. This graft polymer is a melt film that self-polymerizes during application and includes oligomeric material, which would not be suitable for food contact applications considered in the present invention.
Walker (U.S. Pat. No. 4,806,581) teaches a graft copolymer prepared through bulk polymerization. While this reference includes unspecified fluoroacrylates as one of the potential monomers, the bulk polymerization pathway is the primary teaching, which is not physically realistic for preparation of polymers of the present invention. Others teach about block copolymers of fluoroacrylates for treatment of textiles (U.S. Pat. Nos. 6,855,772, 6,617,267, 6,379,753), however, these graft copolymers, which may contain fluoroacrylates, are prepared based on monomeric or polymeric maleic anhydride. The maleic anhydride creates the reactive bonding site to textile fibers. These reactive groups present an inherent instability in treatment solutions, and are hence at a disadvantage from the present invention.
Relative to the present invention, Miller et. al. (U.S. Pat. No. 5,362,847) teaches a graft copolymerization utilizing an ethylene oxide and/or propylene oxide trunk onto which is grafted a fluoroacrylate monomer. The resulting graft copolymer is then combined with a cross-linking agent to create a durable coating. Unlike the present invention, this reference conducts the graft polymerization in a toxic organic solvent, such as xylene. Removal of organic solvents from the resulting polymers is problematic, with residual solvent being a regulatory concern.
US Patent Application Publication US 2005/0096444 A1 to Lee et al. discloses a graft copolymer created from an assembly of vinyl containing monomers and macromonomers. This is similar in character to Kang-gen Lee's work referenced earlier. These macromonomer polymers are polymerized in a toxic organic solvent after functionalization of the macromonomer with acid chloride. The hydrocarbon trunk chain assembled as a result of the organic solvent polymerization does not contain hydroxyl groups nor is it capable of acting as a self-emulsifying agent as described in the present invention.
The use of cerium as an initiator for use in creating graft copolymers is disclosed in U.S. Pat. No. 2,922,768. Cerium initiation has been broadly used for the grafting of natural polymers, such as starch and cellulose (U.S. Pat. Nos. 4,375,535, 4,376,852, 5,130,394, and 5,667,885), however, the incorporation of fluorinated functionality has not been disclosed.
3. Problems Solved by the Invention
The benefits of substrate treatment by fluorochemicals are widely appreciated. A difficulty often arises in the treatment of the substrate to produce those benefits. The present invention solves the problem of the use of emulsifiers to effect the emulsion polymerization of many commercial fluorinated copolymers. These emulsifiers can interfere in numerous ways to reduce the performance of the fluorinated copolymer on a substrate. The present graft copolymer also solves the problem of having good bonding to substrates, through the trunk polymer's hydrogen bonding capacity. The need for good hydrogen bonding co-monomers, such as acrylamide, which has regulatory concerns, is reduced or eliminated. In addition, decreasing the degree of hydrolysis of the trunk polymer can be used to improve adhesion to hydrophobic surfaces. The present invention is also capable of delivering advantageous performance from fluorinated vinyl monomers of a wide variety of perfluorinated chain lengths, due to the structure of the grafts. Fluorinated copolymer performance can suffer when the fluoroalkyl chain length is shortened in conventional polymers. The present invention reduces or eliminates the need for co-solvents that increase the hazardous volatile organic compound content of other fluorinated copolymers.
The fluorinated graft copolymer of the present invention solves the problem of incorporating co-monomers of widely divergent reactivity ratios to vinyl perfluoroacrylates, in that the graft polymerization technique can be applied to the present invention multiple times. This allows for incorporating a wide variety of copolymers along one trunk polymer without the difficulties normally experienced during a conventional polymerization. The present invention also solves the difficult problem of how to incorporate grafts along an existing trunk chain. There is no need to use dangerous, highly reactive intermediates such as acid chlorides to create these grafted chains.
The fluorinated graft copolymer of the present invention may reduce the need to use toxic and/or volatile organic compound (V.O.C.) contributing organic solvents to affect the polymerization of the fluorinated copolymer, because the continuous phase is water. Hence these graft copolymers are inherently miscible in nearly all treatment systems, as these are primarily aqueous-based. The fluorinated graft copolymer of the present invention may extend the range of application of repellent treatment by eliminating the need to heat cure the treated substrate after treatment in order to develop the desired repellency properties.